CM2012 introduces to us the ability to easily script many labour-intensive tasks. I was recently adding numerous boundaries to a ConfigMgr implementation for a client so decided the best approach was to automate this procedure.  I fired up the Powershell session from within ConfigMgr and checked the syntax for New-CMBoundary. Now, I had a spreadsheet with a bunch of IP subnets in CIDR notation so it made sense to use this for my script. Running Get-Help New-CMBoundary I got the following:

Example 1: Create a new IP Subnet site boundary

PS C:\>New-CMBoundary -DisplayName "IPSubNetBoundary01" -BoundaryType IPSubNet -Value "172.16.50.0/24"
BoundaryFlags: 0
BoundaryID: 6338009
BoundaryType: 0
CreatedBy: Contoso\PFuller
CreatedOn 6/10/2012 1:17:42 PM
DefaultSiteCode:
DisplayName: IPSubNetBoundary01
GroupCount: 0
ModifiedBy:
ModifiedOn:
SiteSystems:
Value: 172.16.50.0/24

Looks straightforward enough but no. This simply doesn’t work as stated. The problem seems to be that it doesn’t understand the ‘/24’ part (in this example). Instead, what you first need to do is to find the subnet ID which is associated with your address. If you’re unsure what this is then I’d recommend you use something like http://www.subnet-calculator.com/cidr.php:

In the example above we have a CIDR range of 10.13.160.0/23. You can see from the calculator that this produces a network ID of 10.13.160.0. Therefore the correct syntax for New-CMBoundary is as follows:
New-CMBoundary -DisplayName “IPSubNetBoundary01” -BoundaryType IPSubNet -Value “10.13.160.0”
All that said, I’d personally avoid IPSubnet boundaries completely. Instead, just go for a range, far simpler to understand. The CIDR calculator is again helpful for this and displays the range at the bottom.
Thankfully, the IPRange syntax is correct so you shouldn’t have any issues.